There has conventionally been proposed a technique of assigning a document ID to a document read by a digital copying machine, printing the document with the document ID, and registering the data in an HDD (Japanese Patent Laid-Open No. 10-308868). According to this technique, document data which is registered in the HDD by reading again the document printed with the document ID, and the document is printed again.
This technique is targeted at a document read by a copying machine, but can also be applied to a case wherein print data from a host computer is printed by a printer. In this case, print data is held in the memory of the printer, a document ID is assigned to the print data, and then the print data is printed. The printed product is read by another copying machine, read out from its memory, and reused.
However, the latter system cannot attain the effects of the technique if a printer which is intended by the user to print target data does not have the above-mentioned functions of holding print data and assigning a document ID.